As discussed in U.S. Pat. Nos. 4,198,037 and 4,566,678 to David Anderson and assigned to the assignee of the present application, and Defensive Publication Number 190960 to Dominic Bianca and assigned to E. I. du Pont de Neumours & Co., thermoplastic elastomers have been widely used for the manufacture of compression springs. The thermoplastic elastomer discussed in these references is a copolyester polymer elastomer such as sold by E. I. du Pont de Nemours & Co. of Wilmington, Del., under the Trademark "HYTREL".
Generally, this type of polymer elastomer material has inherent physical properties that make it unsuitable for use as a compression spring. However, as noted in the above cited references, a method is set forth whereby copolyester polymer elastomer material can be treated for rendering the material usable for the manufacture of a compression spring.
This invention continues with the experimentation and development of physical modification of the elastomer block before the application of a compressive force as set forth in the above noted references. An objective is to tailor the shape of the starting material in order to produce a spring having a given spring rate. For example, when designing an elastomer spring, it is often necessary to incorporate a number of serially arranged subsidiary spring elements to satisfy the desired spring characteristics, all within a predefined envelope or space. This serial arrangement requires some method of segmenting or separating the subsidiary spring elements within the envelope.
Previous methods have generally relied on separate parts, such as steel plates, to either physically separate or segment the required subsidiary spring elements. These methods generally include a number of inherent disadvantages. First, the necessity and expense of the segmentation or seperation elements themselves. Second, the added complication and expense of assembling the various parts. The Bianca reference achieves spring rate modifications by securing steel disks around a "HYTREL" block followed by compression. The result is a segmented column spring wherein each segment is separated by a steel disk. The Anderson U.S. Pat. No. 4,566,678 provides a central core or opening in an individual copolyester elastomer body, before the application of an axial compressive force to achieve variations in spring characteristics. The individual subsidiary spring elements are then stacked to comprise a segmented column for use as a spring.
The invention hereunder consideration is directed to a segmented or separate energy-absorbing unit, formed from a single elastomer block. The current design overcomes the above noted disadvantages by using the elastomer itself to accomplish the segmentation of the spring into its subsidiary spring elements. By increasing the cross-sectional area of an elastomer tube at the desired segmentation locations, the initial structure of the tube or perform may be configured such that when subjected to axial compression a number of distinct subsidiary spring elements will be created between the segmentation locations. The extra elastomeric material located at the segmentation points serves to constrain the elastomer during axial compression and greatly reduce the deformation, both axially and radially, at these locations. Neither additional parts nor assembly are required. The segmentation of the single elastomer block into a series of subsidiary spring elements is achieved without the aid of steel retaining rings or other external means. In practice, a hollow elastomer tube is manufactured which includes ring or donut portions (of additional cross-sectional area) encircling the tube at the points of desired segmentation. The block or tube is then subjected to axial compressive forces as described in the above identified U.S. Patents to Anderson, the disclosures of which are incorporated herein by reference. As is apparent, the resultant product is a single unitary member through which fluid may pass without the problem of leakage through the side walls. Thus, it may function additionally as a subassembly in a seal or accumulator.